Results from epidemiological studies have provided clues as to etiological factors involved in the development of large bowel cancer in man. Preliminary studies in metabolic epidemiology have shown that the high fat/meat diet plays a modifying role in the activity of intestinal bacteria and in the composition of cholesterol metabolites and bile acids which can act as cocarcinogens for the colon. The overall objective of this project is to delineate the relationship among dietary components, intestinal cholesterol metabolites and bile acids, activity of intestinal microflora and colon cancer in man, and to identify a biochemical indicator for colon cancer. Fecal samples analyzed so far indicate that the patients with colon cancer, polyps or ulcerative colitis excreted high amounts of bile acids and cholesterol metabolites and had high fecal bacterial 7 alpha-dehydroxylase and cholesterol dehydrogenase activity compared with the controls.